There are two primary objectives of this study. The first is to investigate the efficacy of aspirin and of folic acid supplementation in preventing the recurrence of neoplastic polyps of the large bowel with a randomized, double blind, placebo controlled clinical trial. The principal aim is to test that hypothesis that aspirin taken orally (either 80 mg. or 325 mg. daily) will reduce the occurrence of neoplastic polyps among those with a recent history of these tumors. The second primary objection is to test whether folic acid supplementation (1 mg daily) will reduce the occurrence of neoplastic polyps among those with a recent history of these tumors. The secondary objectives are 1) to contrast the effects of the two aspirin doses on adenoma recurrence, 2) to investigate the relationship between assignment to aspirin and the number and size of recurrent polyps, and 3) to investigate the relationship between assignment to folic acid and the number and size of recurrent polyps. Preliminary determination ofpatient eligibility will be made through review of medical records and contact with the patient's physician. A clinical coordinator will discuss the study with potential subjects and obtain informed consent. The allocation scheme will be accomplished using a computer generated, random number table. Folate will be assigned randomly using a 2X3 factorial design. Patients will not be asked to participate in the study unless the patient's physician has given approval. Subjects will not receive monetary compensation for participation in this study. There will be no additional cost to the patient for participation in the study. In this study, all raised mucosal lesions will be excised and biopsied, their location and size noted and pathology material sent to the pathology center for confirmation of diagnosis. Microscopic slides will be collected by the coordinating center and will be sent to the University of Minnesota for review. The principal end point is the occurrence of neoplastic polyps of the large bowel in the interval between randomization and the three year colonoscopy. Data from previous studies by this group indicates a three year recurrence of slightly over 59%. This protocol is in progress, no results are available. Should the treatment prove effective in preventing cancer, the public will clearly benefit. The potential benefit of a simple, safe, and inexpensive prophylactic is clear.